Manufacture of collagen fiber material



Patented Dec. 27, 1%56 3,294,581 MANUFACTURE OF CGLLAGEN FIBER MATERHAL Laurence R. B. Hervey, Concord, and John R. Starr, Belmont, Mass, assignors, by mesne assignments, to United Shoe Machinery Corporation, Flcmington, N.J., a corporation of New Jersey No Drawing. Filed .iune 14, 1965, Ser. No. 463,910 3 Claims. (Cl. 117140) This invention relates to an improvement in the manufacture of collagen fiber based material and particularly to an improved method for the manufacture of a strong leather-like material.

In the copending application of Shu-Tung Tu Serial No. 256,225, entitled, Leather-like Material and Method of Making the Same, which was filed February 5, 1963 and is now U.S. Patent No. 3,223,551, there is disclosed the manufacture of a leather-like material in which undissolved collagen fibers are associated with a. layer of intermeshed fibers by introducing an aqueous suspension of collagen fibers into an intermeshed fiber mass. The collagen fibers in suspension are slightly swollen and of microscopic size, and are retained within the intermeshed fibrous mass and caused to associated with each other as a larger collagen fiber structure extending through the intermeshed fibrous mass to reinforce those fibers against displacement.

Achievement of best results by the process of the above-referred to application calls for a careful balance between using a pH value displaced enough from the isoelectric point of the collagen fibers to secure good penetration ability and securing good collagen fiber retaining ability through use of a pH value as close to the isoelectric point as will permit efi'ective entry of the collagen fibers in suspension into the intermeshed fiber mass. With some collagen fiber suspensions, achievement of good penetration and good collagen fiber retention is achieved only within a narrow range of pH values, in some instances only 0.1 pH unit. Such close pH control is dilficult to achieve particularly in larger operations and in many instances best collagen retention must be sacrificed in the interests of better penetration.

It is an object of the present invention to provide a method for introducing and retaining collagen fibers into a mass of intermeshed fibers under conditions allowing a broader range of pH values and a greater latitude in the character of the collagen fibers for securing effective penetration and high collagen fiber retention.

To this end and in accordance with a feature of the present invention an aqueous collagen fiber suspension is prepared and there is added to the suspension a small percentage of deacetylated karaya gum. Surprisingly, even though the viscosity of the collagen fiber suspension is increased, rapid and uniform penetration is secured even at pH values close to the isoelectric point, while at the same time there is also achieved excellent collagen fiber retention within the intermeshed fiber mass.

A suspension of microscopic size collagen fibers for use in the present process may be formed according to the procedure and conditions set forth in the copending application above referred to. That is skin material preferably is lightly tanned to an extent comparable to tion in forming short fibers of microscopic size for penetration into intermeshed fiber masses. The beating of the skin material is carried to an extent to form distinct noncolloidal fibers which have a length of from about 0.001 mm. to not over about 4 mm. in length, preferably not over 1 mm. in length. The suspension obtained is then adjusted in pH above or below the isoelectric range of the collagen fibers to efiect swelling of the fibers. The term swelling in the sense here intended refers to the phenomenon that the surfaces of the fibers become slippery and the fibers increase in thickness and decrease in length but remain at distinct fibers.

It has now been found that the requirements for control to secure optimum penetration and retention of collagen fibers in an intermeshed fiber mass may be made much less exacting by combining a small percentage of a deacetylated karaya gum with the collagen fiber suspension.

Karaya gum is the dried exudation of Sterculia, e.g. Srerculz'a urens and Cochlospermum belonging to the family Bixaceae. It is a complex polyacetylated polysaccharide of high molecular weight. It is insoluble in Water but imbibes water to form a jelly. The gum is readily hydrolyzed by treating an aqueous dispersion with a mild alkali, preferably ammonia, to replace acetyl radical constituents. The resulting deacetylated karaya' gum [forms a viscous slippery aqueous dispersion. The deacetylated karaya gum exhibits marked polarity presumably because of free OH groups.

In general at least about 1% of the deacetylated karaya gum is used to give substantial improvement; but it is preferred to use from 5% to 10% by Weight of deacetylated karaya gum based on the weight of the collagen fibers in suspension.

Penetration of a collagen fiber suspension into an intermeshed fiber mass and retention of the collagen fibers by the intermeshed fibers is afiected by the character and extent of swelling of the collagen fibers which depends on the pH of the suspension and the extent of tanning of the collagen, and is also aflected by the concentration of the collagen fibers in the suspension and the openness of the intermeshed fiber mass.

A useful degree of swelling of the suspended collagen fibers is obtainable at pH values about 0.5 of a pH unit outside the isoelectric range of the collagen fiber. Where the collagen fiber is obtained from hides which have been limed, the isoelectric range may be from about 4 to 5.5 while with hides which have not been limed the isoelectric range may be from about 7 to about 8. Or dinarily limed hides which are more readily available will be used and the following description sets forth conditions particularlyuseful with fibers from limed hides. Adjustment of pH values for use with fibers from other hide materials can be made readily by chemists. On the acid side of the range the pH of the suspension of collagen fiber from limed hide will ordinarily be kept in the range of from about pH 0.5 to about pH 3.5 and most desirably from about pH 2 to'about pH 3.0 The higher portions of this range are used with the more highly swelling acids such as formic acid, acetic acid, citric acid, phosphoric acid and others.

Efiective swelling above the isoelectric range has been obtained in a suspension of collagen fiber from limed hide at a pH in the range of from about pH 6.0 to about pH 12 and more desirably from about pH 8 to about pH 10. The fiber suspension may be brought to this range by addition of alkaline reagents such as sodium hydroxide, trisodium phosphate, potassium hydroxide and various other alkaline hydroxides and salts which do not form. insoluble compounds with the collagen.

Penetration ability decreases and retention of the fiber increase with increases in the extent of tanning. It has been found generally desirable to use collagen fiber tanned is reduced to a relatively low percentage.

to an extent corresponding to about 0.2% to about 1.1% formaldehyde by weight based on the weight of the collagen fiber. Thus, it has been found that with a formaldehyde content of 0.2% by weight based on the weight of the hide material, the fiber suspension at the important pH range penetrates well into a given fiber batt but that retention of thefibrous material in the batt is barely acceptable. Where the formaldehyde content is 1.1% by weight based on the weight of the hide material and where no deacetylated karaya gum is used, a proportion of the fibers may be retained on the surface of the same fiber batt to which the suspension is applied and the penetration properties are poor. Within this range and preferably at a formaldehyde content of from about 0.4 to about 0.6% by weight based on the weight of the hide material and with close control of the pH of the suspension, suspensions penetrate well and the fibers are retained effectively within the fiber batt. It is desirable that the fibers have been swollen to a controlled degree and it is believed that one effect of this swelling is a plasticizing of the fibrous collagen material enabling the fibers to move effectively through the interstices in the fiber batt. Higher tanning agent contents restrain the extent of swelling to reduce the ability of the fibrous material to enter the batt; and if no tanning agent is used, there is not only an undesirable increase in viscosity which makes it difficult to use it to penetrate a fiber batt but the fibrous material is not retained well by the fibers of the batt.

There is some indication that, at least with the more highly tanned collagen fibers, for example, fibers contain ing from about 0.6% to about 0.8% by weight formaldehyde based on the weight of the fibers, the swelling may occur primarily at the surfaces of the fibers. This offers the advantage that the fibers develop a surface character allowing the fibers to slip relative to one another and to the fibers of the mat so that the fibers will penetrate the fiber mat, while the volume of individual fibers is not greatly increased so that the ultimate quantity of collagen fiber solids on a dry fiber basis which can be introduced into a mat to fill the interstitial spaces in the mat may be greater with the more highly tanned fibers than with the less tanned fibers. It is believed that the deacetylated karaya gum added to a collagen fiber suspension becomes associated to some extent with the collagen fibers surfaces to provide a slip effect to aid penetration of fibers, for example, fibers tanned to the higher ranges, which might not be sufficiently swollen for effective penetration.

The ability of suspended fibers to penetrate an intermeshed fiber mat depends also on the retained openness of a mat during application of the collagen fiber slurry or suspension. Fiber mats which retain a high degree of openness may be penetrated with collagen fiber suspensions with a degree of tanning and under pH conditions giving a relatively low penetrating ability which would not effectively enter less open fiber mats. It is possible to form fiber mats filled with collagen fibers by adjusting the penetrating ability of the collagen fiber suspension through careful control of extent of tanning and pH conditions relative to the retained openness of the fiber mat. However, the precision of control required is much less where deacetylated karaya gum is included in the suspension.

In addition to the factors of extent of tanning and pH control which exert a primary effect on the penetration ability, a limited control over penetrating ability can be obtained by adjusting the collagen fiber solids content of a suspension. That is, suspensions of collagen fibers with relatively low penetrating ability may penetrate more effectively where the collagen fiber solids content Suspensions having collagen fiber solids contents of at least 0.5% preferably from about 1% to about 5% are preferred from the standpoint of securing a good penetration and the introduction of a desired high collagen fiber solids content into a fiber mat with desirable efficiency in time and amount of suspension handled. It will be understood that it is possible to operate somewhat outside those ranges; but, for example, the use of a lower solids content suspension entails the separation of collagen fiber from a large volume of liquid; and use of a higher solids content suspension may require an undesirably open mat or result in uneven penetration.

The use of deacetylated karaya gum is more important with high collagen fibers content suspensions. As discussed above suspensions having a higher content of collagen fibers tend to penetrate intermeshed fiber masses less effectively than do low collagen fiber content suspensions so that as discussed above undesirably open mats have been required or uneven penetration has been secured. Surprisingly the deacetylated karaya gum appears to have proportionately greater effectiveness with the higher collagen fiber content suspensions and thus increase the efficiency of the process and insure high collagen fiber retention within the intermeshed fiber mass.

It is believed that the deacetylated karaya gum acts as a protective colloid. Protective colloid action ordinarily involves an electrical charge effect on the particles which prevents their association. The deacetylated karaya gum is relatively rich in alcoholic OH groups which tend to develop a net negative charge at the surface of the particle. Also in addition the deacetylated karaya gum molecule is swollen and hydrated by the water and there is some indication that the water of the swollen molecule may have some effect in establishing hydrogen or hydration bonding between the deacetylated karaya gum molecule and the hydrated surface of the collagen fibers. Particularly in alkaline media, the result of such association is a high negative charge on the associated collagen fiber and protective colloid which tends to keep the collagen fibers'apart and resist premature tangling or packing together of collagen fibers in the course of penetration into an inter-meshed fiber mass. The electrical charge effect is supplemented and assisted by the covering or masking of portions of the collagen fibers by hydrated colloid material on its surface which also tends to prevent tangling or packing of the fibers. A further action is a marked increase in the viscosity of the collagen fiber suspension which slows down movement of the fibers relative to each other 'in the suspension medium and thus reduce the frequency and speed at which collagen fibers approach each other to reduce the tendency to tangle or pack. Finally colloid material on the surface of the collagen fibers is slippery and may serve to help the collagen fibers to move into an intermeshed fiber mass.

The above discussion is advanced as of possible assistance in understanding the invention; but it is to be understood that patentability does not depend upon the correctness of the explanation advanced for the advantages obtained.

A wide variety of intermeshed fiber materials both woven and nonwoven may be used for association with collagen microscopic fiber suspensions. Ordinarily nonwoven fiber materials are preferred because of their greater variety of thicknesses, densities and openness to penetration by the suspensions. Thus, the fibers may be nylon, polyacrylic ester fibers (Orlon), polyester fibers (Dacron), polypropylene fibers, wool, extruded cellulosic fibers such as viscose or cellulose acetate and others. It has been found that best results are secured when the fibers are hydrophobic. In this connection a batt of longer collagen fibrous material which has been treated for example, by chrome tanning or other treatment to decrease its affinity for water may be used. Also natural cotton fiber preferably treated to decrease its affinity for water is also usable.

Since an important aspect of the present invention is the manufacture of leather-like products, the intermeshed fiber materials are preferably in the form of relatively solids.

thin batts in which the fibers are in a relation providing relatively large interstitial spaces. The fiber batts preferably although not necessarily have been subjected to a treatment as with barbed needles to improve the intermeshing of the fibers. A fiber density and relation which have been found very satisfactory are those in nylon fiber batts having densities of the order of 4 oz. per sq. yd. at a thickness of 0.15" and 6 oz. per sq. yd. at a thickness of 0.175". It is preferred that the fibers be relatively fine and fall in the range of from 1 to 5 denier with 3 denier being satisfactory. Another highly satisfactory material is a polypropylene fiber batt having a density of 7 oz. per sq. yd. and a thickness of 0.2.

Penetration of the suspension of swollen collagen microscopic fibers into an intermeshed fiber mass may be effected in a variety of ways. Thus, a fiber batt may be immersed in a suspension, suitably a relatively low solids suspension of the order of 1% to 3% by weight The rate of impregnation may be increased by use of a vibrator. Another procedure involves disposing the fiber batt on a screen and forcing the suspension in with the aid of pressure or suction. Suspensions having a solids content of for example, from about 1% to about 5% by weight solids may be used in this procedure. Still other procedures are available including spreading the suspension on the surface of the batt and working it in.

Products having a higher collagen content at the surface may be formed by first treating the fiber batt with a collagen suspension having good penetrating ability and thereafter treating the batt with a suspension having a lower penetration ability. If desired suspension may be applied from alternate sides.

When the intermeshed fiber mass impregnated with collagen fiber is treated to reduce swelling either by pH change, extraction with water or solvent or the like as described more fully in the copending application abovereferred to, there is an observable association of the fibers into substantially aligned relationship. It appears that as association of the individual fibers proceeds, a larger collagen fiber structure is reaggregated from a multitude of the microscopic fibers and is comparable to native larger collagen fibers extending through the intermeshed fiber mass.

Reduction of the acid or alkali content of the collagen microscopic fiber material within a fiber mass and removal from the fibers of the water of swelling may be effected by subjecting the fibrous mass to extraction with distilled water or a water-miscible volatile organic solvent such as acetone and other ketones, and lower alcohols such as methanol, ethanol and isopropanol to bring the pH to the isoelectric range. Treatment of the fiber batt with an aqueous solution of a buffer salt such as an acetate or phosphate buffer system is also effective to bring the pH to a value in the range of about 3.5 to about 6 at which reaggregation of the collagen microscopic fibers will occur with removal of the swelling water from the fibers. It is desirable in the use of buffer systems to use a solution having an ionic strength of about 0.2. Rea'ggregation may also be effected by treating the fiber batt with a 10% aqueous ammonium sulfate solution which effects a deswelling of the fibers.

The fiber batt is compacted and reduced in thickness in the course of penetration by the suspension and reaggregation of the collagen material so that, for example, starting with a 4 oz. per sq. yd. nylon fiber batt with an initial thickness of 0.15", after penetration by suspension and reaggregation of the collagen material, the thickness will have reduced to from about .015 to about .03. Correspondingly, a sheet prepared from a 6 oz. per sq. yd. nylon batt having an initial thickness of 0.175 will form a Sheet about 0.04 inch in thickness. This reduction in thickness is due in considerable measure to the action of the suspension in being forced into the batt. A further action which influences the reduction in thickness is the pulling together of the collagen material by water bond- 6 ing; and this factor may range from very slight where water is extracted from the sheet by solvent to relatively large where a substantial portion of the water is removed by evaporation.

The sheet material is preferably subjected to tanning with mineral tanning agents such as chrome tanning liquors or with vegetable tanning agents. Because of the collagen deswelling action of mineral tanning agents such as chrome tanning agents it is possible to effect both reaggregation and tanning with such agents. Conventional leather tanning procedures may be used and the tanning may be carried out either in an aqueous tanning medium or a solvent type tanning medium.

The following example is given to aid in understanding the invention and it is to be understood that the invention is not restricted to the particular materials, proportions or procedures set forth therein.

Example I Pickled hide splits were washed and 35% of the washed material was introduced into a drum along with a buffer made of 1200 ml. of glacial acetic acid, 1000 gins. of sodium hydroxide and 1000 ml. of a 37% solution of formaldehyde. lbs. of water were added and the drum was rotated for 21 hours. The splits were then drained, washed for one hour, horsed and drained for one-half hour and then cut into approximately one inch pieces. The chopped material was then introduced into a Hollander type paper beater and made up to a 200 lb. batch by addition of water. The pH of the material in the beater at this time was about 5.4. The beater was operated until about 4 kw. hours of energy had been supplied to the beating operation. At this time, 250 cc. of an emulsifying agent were added and beating continued for three minutes to emulsify the fat content of the Split material. The resulting emulsion was drained off. Half of the split material was then put back in the beater along with 80 lbs. of water and the beating was continued. The pH of the material was adjusted to approximately pH 7 by addition of 4 N solution of sodium hydroxide. After 4 /2 hours of beating the material was reduced to a suspension of collagen fibers having a length of about 0.2 to about 1 mm. The collagen fibers had a formaldehyde content of about 0.21% by weight based on the weight of the dry collagen.

Two parts of karaya gum were finely granulated and combined with one hundred parts of water to form a jelly. A small amount of ammonia was added to bring the pH to about 6 and the mixture was allowed to stand about three hours. At the end of this time it was found that the material had changed from a gel-like material to a viscous slippery liquid indicating hydrolysis of the gum to replace acetyl radical constituents of the karaya gum molecule without substantial alteration of the molecular structure of the gum.

Quantities of the collagen fiber suspension were withdrawn and made up with addition of water or by addition of water and the ammonia treated karaya gum (deacetylated karaya gum), to the solids content and deacetylated karaya gum contents shown in the following table. The percent of the deacetylated karaya gum given in the table is percent by weight based on the weight of the collagen fiber solids in the suspension so that for example, a composition listed as 2% solids and 5% karaya gum would contain 5% of 2% or A of deacetylated karaya gum based on the weight of the suspension. Portions of the suspensions were made up to a range of pH values from pH 2 to pH 10 by addition of acid or alkali and the portions were supplied to the surfaces of sections .of a 6 oz. per sq. yd. mat of 3 denier nylon fiber, the mat having been needled, to determine the abilities of the various portions to penetrate the mats.

Penetration of the mats was effected by disposing the sections of mat on a filter .bed provided with means for applying suction. When portions of fiber suspension on the surface of the mat had been leveled with a rubber squeegee suction was applied tending to pull the suspension into the mat.

TABLE I In the above table the portions of the pH range with lattice cross hatching indicate areas in which penetration of the collagen fiber suspension into the intermeshed fiber mat was unsatisfactory. Uncross-hatched portions of the pH range indicate pH values at which good penetration of the suspension into the intermeshed fiber mat was obtained.

It will be observed that the collagen fiber suspension not containing deacetylated karaya gum had a wide range of pH values in which the penetration ability was unsatisfactory. On the other hand the suspension in which deacetylated karaya gum is present penetrates effectively into an intermeshed fiber mat at pH values not workable with simple collagen fiber suspension.

The fiber mats which had been penetrated by collagen fiber suspensions were recluceable to tough leather-like sheet materials by procedures such as shown in the copending application above-referred to. Such further processing may include drawing dry acetone through the impregnated mat to effect a reaggregation of the microscopic collagen fibers of the suspension and tanning the solvent dried sheet in a standard buffered chromium tanning liquor containing 0.5% chrome calculated as Cr O and 1% of sodium formate and having a pH of 4. The sheets after removal from the tanning may be allowed to stand overnight in a covered receptacle and washed in water for three successive periods of 15 minutes. The sheets may then be dried and immersed in a 4% by weight solution of oleic acid in acetone for 1 /2 hours. On removal from the oleic acid solution and drying, the sheets have physical properties comparable to chrome tanned leather. The sheet material may be given any treatment to provide a suitable finish.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is:

1. The process of forming a tough, flexible material which comprises the steps of applying to intermeshed open fiber mass in penetrating relation an aqueous suspension containing from about 1% to about 5% by weight based on the weight of the suspension of swollen, distinct, fine, collagen fibers of microscopic size to carry said collagen fibers into the interstitial spaces of said intermeshed fiber mass, said suspension containing at least about 1% by weight of deacetylated karaya gum based on the weight of collagen fibers in said suspension, said deacetylated karaya gum cooperating with said collagen fibers to resist packing together of said collagen fibers, and removing the swelling water from collagen fibers within said intermeshed fiber mass to reaggregate them into a larger collagen fiber structure within the interstitial spaces throughout said mass of intermeshed fibers to reinforce said intermeshed fibers against displacement.

2. The process of forming a tough, flexible material which comprises the steps of applying to an intermeshed open fiber mass in penetrating relation an aqueous suspension containing from about 1% to about 5% by weight based on the weight of the suspension of swollen, distinct, fine, sh-ort collagen fibers from 0.001 to about 4 mm. in length to carry said collagen fibers into the interstitial spaces of said intermeshed fiber mass, said suspension containing at least about 1% by weight of deacetylated karaya gum based on the weight of the collagen fibers in said suspension, said deacetylated karaya gum being associated with said collagen fibers to resist packing together of said collagen fibers, said suspension being caused to penetrate said intermeshed fiber in quantity to provide from about 5% to about by weight of collagen fibers based on the combined weight of said intermeshed fibers and said collagen fibers, and removing the swelling water from collagen fibers within said intermeshed fiber mass to reaggregate them into a larger collagen fiber structure within the interstitial spaces throughout said mass of intermeshed fibers to reinforce said intermeshed fibers against displacement.

3. The process of forming a tough, flexible material as defined in claim 2 in which said suspension contains from 5% to 10% by weight of deacetylated karaya gum based on the weight of the collagen fibers in said suspension.

References Cited by the Examiner UNITED STATES PATENTS 2,040,511 5/1936 Bleyenheuft 117164 X 2,405,978 8/1946 Pickles et al. 117-140 X 2,838,363 6/1958 Veis et al. 106-124 X 2,934,446 4/1960 Highberger et al. 162151 X 2,934,447 4/ 1960 Highberger et al. 162151 X 3,073,714 l/l963 Tu et al. 117l1 3,223,551 1/1965 Tu l17140 WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner. 

1. THE PROCESS OF FORMING A TOUGH, FLEXIBLE MATERIAL WHICH COMPRISES THE STEPS OF APPLYING TO INTERMESHED OPEN FIBER MASS IN PENETRATING RELATION AN AQUEOUS SUSPENSION CONTAINING FROM ABOUT 1% TO ABOUT 5% BY WEIGHT BASED ON THE WEIGHT OF THE SUSPENSION OF SWOLLEN, DISTINCT, FINE, COLLAGEN FIBERS OF MICROSCOPIC SIZE TO CARRY SAID COLLAGEN FIBERS INTO THE INTERSTITAL SPACES OF SAID INTERMESHED FIBER MASS, SAID SUSPENSION CONTAINING AT LEAST ABOUT 1% BY WEIGHT OF DEACETYLATED KARAYA GUM BASED ON THE WEIGHT OF COLLAGEN FIBERS IN SAID SUSPENSION, SAID DEACETYLATED KARAYA GUM COOPERATING WITH SAID COLLAGEN FIBERS TO RESIST PACKING TOGETHER OF SAID COLLAGEN FIBERS, AND REMOVING THE SWELLING WATER FROM COLLAGEN FIBERS WITHIN SAID INTERMESHED FIBER MASS TO REAGGREGATE THAM INTO A LARGER COLLAGEN FIBER STRUCTURE WITHIN THE INTERSTITIAL SPACES THROUGHOUT SAID MASS OF INTERMESHED FIBERS TO REINFORCE SAID INTERMESHED FIBERS AGAINST DISPLACEMENT. 